Co-extrusion of periodically modulated structures

ABSTRACT

A method of forming an extruded structure includes dispensing at least a first material through an extrusion head, varying a pressure applied during extrusion of the first material over time, and depositing the first material on a substrate, wherein a width of the first material varies with a pressure forming a stripe of the first material having a varying width along a length of the stripe.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No. 14/010,076 filed Aug. 26, 2013, which is incorporated herein by reference in its entirety.

BACKGROUND

It is possible to extrude pastes and other viscous materials through an extrusion head to deposit the material onto a surface. The process may sometimes be referred to as micro-extrusion to differentiate it from extrusion processes using dies on large machines. The materials exiting the extrusion head are generally referred to as extrudates. The extrusion head typically has at least one input port to receive the material from some sort of reservoir, and at least one output port or die or nozzle to allow the extrudate to exit the head. A pump connected to the reservoir of material controls the flow, which in turn affects the resulting stripe of extrudate.

For most applications, it is desirable that the extrudate stripes have uniform shape and density. Extruded terminology generally refers to a single stripe of material as a one-dimensional structure. Structures having two or more stripes of material are referred to as two-dimensional. It is possible to form limited three-dimensional structures using extrusion heads in multiple passes, but the manufacturability issues and costs make that approach difficult. Hollow cavities, overhangs and other ‘hidden’ features require additional extrusion passes and/or additional processing steps. Generally, two dimensional extruded structures have multiple, linear, stripes of extrudates.

Being able to create features that are more than two-dimensional and not necessarily straight line features with an extrusion head would have advantages in surface area and material utilization for some applications. It is possible to vary the flow of material over time to generate extruded structures that are not linear, uniform stripes of extrudates.

SUMMARY

According to aspects of the present disclosure, there is provided a method of forming an extruded structure that includes dispensing at least a first material through an extrusion head, varying a pressure applied during extrusion of the first material over time, and depositing the first material on a substrate, wherein a width of the first material varies with a pressure forming a stripe of the first material having a varying width along a length of the stripe.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a prior art two dimensional structure.

FIG. 2 shows a prior art two dimensional structure after removal of a sacrificial material.

FIG. 3 shows a three dimensional structure formed in a method according to the prior art.

FIG. 4 shows an embodiment of a near-three dimensional structure of material having varying widths.

FIG. 5 shows an embodiment of a near-three dimensional structure of two materials having complementary patterns of varying widths.

FIG. 6 shows an embodiment of a near-three dimensional structure of three materials.

FIG. 7 shows an embodiment of a system for modulating pressures in an extrusion head.

FIG. 8 shows a graph of paste pressures in an extrusion head.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 shows a two-dimensional structure in accordance with the prior art. It is two-dimensional in that it has at least two stripes of materials. In extrusion, the simplest structures resulting from one circular or rectangular slot in an extrusion head is generally considered to be one-dimensional (1D). The next level of complexity would encompass 2D structures, resulting from extrusion heads that have multiple slots, such as 10 shown in FIG. 1. The same material 14 may be simultaneously extruded from different slots of the same or different forms, or multiple materials such as 12 and 14 could be co-extruded from multiple slots. In some structures, the second material 12 may be sacrificed to form gaps in the structure, where after removal the second material of the structure would then become air, as shown in FIG. 2.

A further level of complexity would be to achieve 3D structures such as 20, typically with multiple passes of the extrusion head to form layers of extruded materials such as 24 and 26. True 3D structures could include hidden features such as voids, overhangs, re-entrant features, etc., typically not achievable using a single pass of an extrusion head. However, it is possible to achieve ‘near-3D’ structures, having higher complexity than simple stripes or runs of multiple materials from a single pass extrusion head.

The embodiments here may be referred to as ‘near-3D’ or 2.5D structures. The features of the resulting stripes of materials are more complex than simple stripes of materials, having varying widths along their lengths. This may be accomplished by varying the pressure used to extrude the materials over time. FIG. 4 shows an embodiment or a representation of such a ‘near-3D’ structure 30. The extrudate stripes 34 have varying width along their length, referred to here as periodically modulated stripes. The stripes may be extruded from a single material 34 from an extrusion head. The varying width may have a periodic pattern as shown, but the varying width may also have a non-periodic, or randomized, pattern. However, the use of a periodic pattern of the first extrudate allows for some variations.

FIG. 5 shows a near-3D structure having extrudate stripes of periodically varying widths. The first extrudate 34 has a first pattern of varying widths. The second extrudate 36 has a complementary second pattern where the wide portions and narrow portions of the second pattern match up to the narrow portions and wide portions of the first pattern. The two patterns are accomplished by periodically modulating the pump differently over time for each pattern. The modulation of the flow of materials over time allows the formation of the patterns.

The two materials may consist of any material that can be extruded through the extrusion head. Typically, the materials are pastes. The materials remain separate from each other. The materials may be a mixture of other materials, but for the purposes of this discussion, when they exit the print head as extrudates they are each one material. Similarly, the two extrudates remain separate from each other, even though they may be extruded together. Some mixing may occur at the material boundaries, but the integrity of each is substantially maintained. One should note that the examples here discuss two materials, but more than two materials may be used.

FIG. 6 shows an example of a near-three dimensional structure having more than two materials. The extrudates 34 and 36 have another extrudate 38 in the structure. The materials are modulated with respect to time as before, but the extrudates 34 and 38 would be modulated in phase with each other to form the patterns that complement the pattern of extrudate 36. For example, the extrudates may form the pattern of extrudate 34, extrudate 36, extrudate 38, extrudate 36, extrudate 34, etc.

The pastes may contain materials which would form electrically conductive or electrochemically active structures, as examples. Electrochemically active materials may be used in electrode structures that make up part of batteries. Non-active materials may be used as filler and then sacrificed. If non-active, or sacrificial, material is used, then once the non-active material is removed, such as be drying, sintering, etc., it can be replaced with another material; but in the instance where no other material is subsequently introduced, then gaps would remain, where the second material would be air.

If for example one of the materials is electrochemically active, a simple model assuming sinusoidal modulation has shown that the resulting structure has approximately 21% greater periphery while having about 10% less average distance between the centerline of an extruded stripe and the nearest border, compared to a conventional linear extruded structure. This increase in surface area, and decrease in the average distance between the interior and border, could for example enhance functional material reaction rates or utilization. Even such a small improvement could be economically significant in a cost-sensitive business such as battery manufacturing.

To vary the widths along the length of the features, the dispensing system uses a pump to create a pressure that then forces the paste out of the extrusion head. One embodiment uses a spool valve to modulate the flow from the pump. Spool valves typically consist of a cylinder housed in a case. The case contains a system of valves that connect to a reservoir and pump on one side. The spools in the valve slide or rotate in the system in response to fluid flow levels to either open or block channels. The fluid from the reservoir flows through the open channels. Typically, spool valves have a controller device that actuates the valve to rotate the spools into the necessary position. FIG. 6 shows an example of this type of system.

In FIG. 7, the motor/pump 40 would connect to the reservoir of material or reservoirs of materials. The controller 46 may control the pump/motor and/or the valve 42. The fluid then flows out of the extrusion head 44 in response to the pressure. In one embodiment, a pressure modulation cycle of 18 milliseconds (msec) is used.

FIG. 8 shows graphical representations of downstream paste pressure responses for rapid partial strokes. Paste #1 is a functional paste in this embodiment, and #2 is a sacrificial paste. Curve 50 is the pressure of paste #1, and curve 52 is for paste #2.

Another embodiment may employ a rotary motor to drive a cam, which in turn would drive a piston. Another piston embodiment may use a linear, moving-coil actuator that would require a mechanical linkage to produce enough force to push on the high pressure paste.

Other variations and modifications exist. The embodiments up to this point have assumed that the materials reside adjacent to each other laterally. It is also possible that the materials can be stacked vertically. Further, the vertical thickness of the materials may be of any thickness. Typically, the thickness may be approximately 10 microns or greater.

It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims. 

What is claimed is:
 1. A method of forming an extruded structure, comprising: dispensing at least a first material through an extrusion head; varying a pressure applied during extrusion of the first material over time; and depositing the first material on a substrate, wherein a width of the first material varies with a pressure forming a stripe of the first material having a varying width along a length of the stripe.
 2. The method of claim 1, wherein varying a pressure comprises modulating a spool valve motor over time.
 3. The method of claim 1, wherein varying a pressure comprises modulating a piston drive over time.
 4. The method of claim 3, wherein modulating a piston drive comprises modulating a rotary motor over time.
 5. The method of claim 4, wherein modulating the rotary motor over time comprises modulating a cam attached to the rotary motor over time.
 6. The method of claim 3, wherein modulating a piston drive comprises modulating a linear, moving coil actuator.
 7. The method of claim 1, wherein dispensing at least a first material through an extrusion head comprises dispensing a first material and a second material.
 8. The method of claim 7, wherein dispensing the first and the second material comprises: modulating pressure over time for the first material in a first pattern; and modulating pressure over time for the second material in a second pattern, wherein the second pattern is complementary to the first pattern.
 9. The method of claim 8, further comprising removing the second material.
 10. The method of claim 9, further comprising filling a space left by removal of the second material with another material.
 11. The method of claim 9, wherein the first pattern has wider and narrower portions and the second pattern has narrower portions that match the wider portions in the first pattern and the second pattern has wider portions that match the narrower portions of the first pattern.
 12. The method of claim 1, wherein dispensing at least a first material through an extrusion head comprises dispensing the first material, a second material and a third material.
 13. The method of claim 1, further comprising performing the dispensing, varying and depositing with the extrusion head at a first position and repeating the dispensing, varying and depositing with the extrusion head at a second position.
 14. The method of claim 13, wherein the second position is adjacent the first position one of either horizontally or vertically.
 15. The method of claim 12, wherein the first and third materials have patterns that are in phase, and the second material has a pattern that is complementary to the patterns of the first and third material.
 16. The method of claim 1, wherein the varying width has a periodic pattern along the length.
 17. The method of claim 1, wherein the periodic pattern is a sinusoidal pattern.
 18. The method of claim 1, wherein the varying width has a randomized pattern along the length.
 19. The method of claim 1, wherein the first material is electrochemically active.
 20. The method of claim 19, wherein the first material forms at least a portion of a battery electrode. 